1. Field of the Invention
This invention generally relates to a method and apparatus for measuring skin moisture by using near infrared reflectance spectroscopy, and more particularly relates to measuring skin moisture without destroying the test object, and producing a portable skin moisture measuring apparatus.
2. Background of the Invention
The skin is a structure consisting of both epidermis and dermis combination. The softness and pliability are the main characteristic factors of skin surface protecting the body and securing the motion of the body. Such characteristic factors are dependent on the amount of moisture contained in the stratum corneum layer, which is the outermost layer of the skin, and controlled by the barrier function and moisture maintaining function of the skin layer.
The stratum corneum is about 20 micron thick, and composed of partially dehydrated cells in a liquid matrix. Between the cells are lipid mixture called stratum corneum intercellular lipid, which composes the barrier of the skin. The lipid mixture is composed of cell amide, cholesterol, free fatty acid, and cholesterol sulfate, secreted from intercellular lamella granular when epidermis cells are transferred from granular layers to stratum corneum, and formed between the stratum corneums.
If normal stratum corneum is not properly developed due to environmental changes and diseases, the barrier function and moisture maintaining function of the skin is lowered. In such situation, the face of the skin becomes easily dried, roughed and cleaved if the moisture of stratum corneum is not sufficiently maintained. Therefore, it is very important to maintain the amount of moisture in the stratum corneum of the skin properly.
However, in modern life, it is difficult to maintain healthy skin due to various pollution and rapid environmental changes. For the above reasons, most people are using a skin moisture lotion in their daily life. In order to maintain healthier skin, it is essential to measure the density of skin moisture and check skin conditions periodically. Although such works can be done by cosmeticians or dermatologist, skin moisture measuring devices are rarely used. Conventional skin moisture measuring devices are utilized at laboratories for research purpose only, because price of those devices are too expensive, and the devices are easily influenced by temperature and humidity changes, which requires to be kept at a constant temperature and humidity conditions.
The infrared spectroscopy and high frequency impedance method are widely used for conventional skin moisture measuring apparatus and method. The infrared spectroscopy is a direct moisture measuring method at certain wavelength range. As the measuring device utilizing the method is not only very expensive because it uses Fourier Transform infrared spectroscopy device using the total reflection absorption method, but also difficult to operate, it is rarely used for commercial purpose devices.
Therefore, devices utilizing the high frequency impedance method have been widely used so far. The devices are utilizing the fact that when a large amount of electrolytes, such as salts and amino acid, are contained in the stratum corneum layer, the electrolytes make the surface of the skin electrically conductive. Therefore, if the alternating current having a constant frequency is applied, electric conductance that is the reciprocal of the resistance that consists of impedance is measured, and the skin moisture is calculated from the electric conductivity that has dependency on the skin moisture.
However, because the conventional skin moisture measuring method using the high frequency impedance method is easily affected by environmental conditions, such as temperature or humidity changes, it does not provide the correct skin moisture value if external environmental conditions change. Moreover, the above method is influenced by the amount of electrolyte that the test skin contains, which is another problem of the skin moisture measuring method using the high frequency impedance method.
Moreover, the size of the conventional skin moisture measuring devices is too big and spacey, and it is too heavy to carry.
The present invention is to provide the method and apparatus for measuring skin moisture by using near infrared reflectance spectroscopy that is improved with respect to the conventional methods and apparatuses.
An object of the present invention is to provide small sized portable skin measuring devices using near infrared reflectance spectroscopy, which is not influenced by environmental conditions such as temperature and humidity changes.
Another object of the present invention is to provide a skin-measuring device that is fast and convenient to use.
These objects may be accomplished with the method and apparatus using Near Infrared Reflectance Spectroscopy (NIRS).
One aspect of the present invention is to provide the method for measuring skin moisture using near infrared reflectance spectroscopy.
A set of reference moisture values of a plurality of sample skin is measured with conventional skin moisture measuring device.
And then providing a set of standard calibration equation of the plurality of sample skin is processed as follows: radiating near infrared on the plurality of sample skin, sensing a set of near infrared reflectance spectra reflecting from the plurality of sample skin, dividing the set of reflectance spectra into a calibration set and a validation set by using random selection, analyzing with multivariate regression the calibration set and the set of reference moisture value to produce a set of standard calibration equation of the plurality of sample skin, and then evaluating and correcting the set of standard calibration equations by using the validation set. Thereafter, the set of standard calibration equations is stored at a memory.
Next step is the process of measuring skin moisture by using near infrared reflectance spectroscopy with reference to the set of standard calibration equation stored at the memory. The process includes radiating near infrared on a test skin, sensing a near infrared reflectance spectrum reflecting from the test skin, and then introducing the near infrared reflectance spectrum from the test skin into the set of standard calibration equations stored at the memory to calculate the skin moisture of the test skin.
Another aspect of the present invention is an apparatus to measure skin moisture using near infrared reflectance spectroscopy comprising the means of storing a set of standard skin moisture calibration equation of the plurality of sample skin, radiating near infrared on a test skin, sensing a near infrared reflectance spectrum reflecting from the test skin, predicting the skin moisture of the test skin from the near infrared reflectance spectrum reflecting from the test skin and the set of standard calibration equation stored at the memory.